How do you create a javascript file?

Welcome to a tutorial on how to create and save files in Javascript. Well, this will be kind of a complicated process for beginners. To keep things simple – Saving files on server-side NodeJS is a breeze, but it is tricky to directly save files on the client-side because of security restrictions. That said, there are many methods we can use.

The possible ways to create and save files in Javascript are:

  1. Use a library called FileSaver – saveAs(new File(["CONTENT"], "demo.txt", {type: "text/plain;charset=utf-8"}));
  2. Create a blob object and offer a “save as”.
    • var a = document.createElement("a");
    • a.href = window.URL.createObjectURL(new Blob(["CONTENT"], {type: "text/plain"}));
    • a.download = "demo.txt";
    • a.click();
  3. Upload the data, save it on the server.
    • var data = new FormData();
    • data.append("upfile", new Blob(["CONTENT"], {type: "text/plain"}));
    • fetch("SERVER.SCRIPT", { method: "POST", body: data });
  4. Create a writable file stream.
    • const fileHandle = await window.showSaveFilePicker();
    • const fileStream = await fileHandle.createWritable();
    • await fileStream.write(new Blob(["CONTENT"], {type: "text/plain"}));
    • await fileStream.close();
  5. In NodeJS, simply use the file system module – require("fs").writeFile("demo.txt", "Foo bar!");

That covers the basics, but let us walk through detailed examples in this tutorial – Read on!

ⓘ I have included a zip file with all the example source code at the start of this tutorial, so you don’t have to copy-paste everything… Or if you just want to dive straight in.

QUICK SLIDES

How do you create a javascript file?

TABLE OF CONTENTS

DOWNLOAD & NOTES

Firstly, here is the download link to the example code as promised.

QUICK NOTES

If you spot a bug, feel free to comment below. I try to answer short questions too, but it is one person versus the entire world… If you need answers urgently, please check out my list of websites to get help with programming.

EXAMPLE CODE DOWNLOAD

Click here to download the source code, I have released it under the MIT license, so feel free to build on top of it or use it in your own project.

All right, let us now get into the various ways to save files in Javascript.

METHOD 1) USE FILE SAVER

1-filesaver.js

<!-- (A) LOAD FILE SAVER -->
<!-- https://cdnjs.com/libraries/FileSaver.js -->
<!-- https://github.com/eligrey/FileSaver.js -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/FileSaver.js/2.0.5/FileSaver.min.js"></script>
 
<script>
// (B) "SAVE AS"
var myFile = new File(["CONTENT"], "demo.txt", {type: "text/plain;charset=utf-8"});
saveAs(myFile);
</script>

Thank goodness, someone did all the hard work. This is one of the easiest and “safest” cross-browser ways to save a file –

  1. Simply load FileSaver.js from the CDN.
  2. Create a new File() object and pop it into saveAs().

METHOD 2) CREATE FILE FROM BLOB & FORCE DOWNLOAD

2-blob-download.html

// (A) CREATE BLOB OBJECT
var myBlob = new Blob(["CONTENT"], {type: "text/plain"});

// (B) CREATE DOWNLOAD LINK
var url = window.URL.createObjectURL(myBlob);
var anchor = document.createElement("a");
anchor.href = url;
anchor.download = "demo.txt";
    
// (C) "FORCE DOWNLOAD"
// NOTE: MAY NOT ALWAYS WORK DUE TO BROWSER SECURITY
// BETTER TO LET USERS CLICK ON THEIR OWN
anchor.click();
window.URL.revokeObjectURL(url);
document.removeChild(anchor);

Due to security restrictions, client-side Javascript cannot directly access the file system. That is, no direct writing and loading of files on the user’s computer. But this is the roundabout way of doing things – Create a BLOB (binary) object to contain all the data, then set a download link to it.

METHOD 3) UPLOAD BLOB TO SERVER

THE JAVASCRIPT

3a-blob-upload.html

<script>
function blobajax () {
  // (A) CREATE BLOB OBJECT
  var myBlob = new Blob(["CONTENT"], {type: "text/plain"});

  // (B) FORM DATA
  var data = new FormData();
  data.append("upfile", myBlob);

  // (C) AJAX UPLOAD TO SERVER
  fetch("3b-upload.php", {
    method: "POST",
    body: data
  })
  .then((res) => { return res.text(); })
  .then((txt) => { console.log(txt); });
}
</script>
<input type="button" value="Go" onclick="blobajax()"/>

THE PHP

3b-blob-upload.php

<?php
echo move_uploaded_file(
  $_FILES["upfile"]["tmp_name"], 
  "demo.txt"
) ? "OK" : "ERROR UPLOADING";

This is an alternative to the above BLOB download – We upload the BLOB and save it on the server instead.

METHOD 4) WRITABLE FILE STREAM

4-file-stream.html

<script>
async function saveFile() {
  // (A) CREATE BLOB OBJECT
  var myBlob = new Blob(["CONTENT"], {type: "text/plain"});
 
  // (B) FILE HANDLER & FILE STREAM
  const fileHandle = await window.showSaveFilePicker({
    types: [{
      description: "Text file",
      accept: {"text/plain": [".txt"]}
    }]
  });
  const fileStream = await fileHandle.createWritable();
 
  // (C) WRITE FILE
  await fileStream.write(myBlob);
  await fileStream.close();
}
</script>

<input type="button" value="Save File" onclick="saveFile()"/>

Yes, the old grandmother’s age of the Internet is over. We can create a file handler and file stream on the user’s computer, use it to save a file. But this still opens a “save file as” dialog box, we cannot directly save without the user’s permission.

P.S. This will only work on Chrome, Edge, and Opera at the time of writing.

METHOD 5) WRITE TO FILE IN NODEJS

5-node.js

// (A) LOAD FILE SYSTEM MODULE
// https://nodejs.org/api/fs.html
const fs = require("fs");

// (B) WRITE TO FILE
fs.writeFile("demo.txt", "CONTENT", "utf8", (error, data) => {
  console.log("Write complete");
  console.log(error);
  console.log(data);
});

/* (C) READ FROM FILE
fs.readFile("demo.txt", "utf8", (error, data) => {
  console.log("Read complete");
  console.log(error);
  console.log(data);
});
*/

Yes, it’s that stupidly simple. Just load the file system module var fs = require("fs"), and use the writeFile() function. To load files, we use the corresponding readFile() function.

COMPATIBILITY CHECKS

  • Blob – CanIUse
  • Create Writable File Stream – CanIUse
  • Show Save File Picker – CanIUse
  • Arrow Function – CanIUse

Not all browsers support the BLOB data type nor all the file writing features. So it is best to do some checks before you enable your ninja features – I will recommend using Modernizr to detect if the browser supports certain features.

  • Javascript Blob – MDN
  • MIME Types – SitePoint
  • Create Object URL and Revoke Object URL – MDN
  • Form Data  – MDN
  • Fetch API – MDN
  • Write Files In NodeJS – Code Boxx

TUTORIAL VIDEO

INFOGRAPHIC CHEAT SHEET

How do you create a javascript file?
How To Save Files In Javascript (click to enlarge)

THE END

Thank you for reading, and we have come to the end of this guide. I hope that it has helped you with your project, and if you want to share anything with this guide, please feel free to comment below. Good luck and happy coding!

How do you write a JavaScript file?

To write a JavaScript, you need a web browser and either a text editor or an HTML editor. Once you have the software in place, you can begin writing JavaScript code. To add JavaScript code to an HTML file, create or open an HTML file with your text/HTML editor.

How do you start a JavaScript file?

To run JavaScript on a browser,.
Open your favorite browser (here we will use Google Chrome)..
Open the developer tools by right clicking on an empty area and select Inspect. Shortcut: F12 . Inspect Browser..
On the developer tools, go to the console tab. Then, write JavaScript code and press enter to run the code..

How create JS file in Windows?

Try NodeJS with Visual Studio Code.
Open your command line and create a new directory: mkdir HelloNode , then enter the directory: cd HelloNode..
Create a JavaScript file named "app.js" with a variable named "msg" inside: echo var msg > app.js..
Open the directory and your app..

What is a JavaScript file?

What is a JS file? JS (JavaScript) are files that contain JavaScript code for execution on web pages. JavaScript files are stored with the . js extension. Inside the HTML document, you can either embed the JavaScript code using the <script></script> tags or include a JS file.